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12.2.1012 · Energy and Respiration

Anaerobic Adaptation of Rice — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 7 parts Lesson 17 of 18 Unit quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

12.2.10 Anaerobic Adaptation of Rice — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how rice survives flooding by getting gas to its roots and tolerating anaerobic respiration.Roots — waterlogged roots do not get the oxygen they need for aerobic respiration…

  • Slow diffusion
  • Rapid upward growth
  • Aerenchyma
  • Ethanol fermentation
  • Toxic ethanol
  • Higher tolerance

Part 1 of 5The problem of flooding

Roots
  • Roots waterlogged roots do not get the oxygen they need for aerobic respiration.
Leaves
  • Leaves submerged leaves do not get the carbon dioxide they need for photosynthesis.
Slow diffusion
  • Slow diffusion oxygen and carbon dioxide diffuse more slowly in water than in air, so they are less available.
Rice
  • Rice has several adaptations that let it survive and grow in waterlogged paddy fields.

Part 2 of 5Adaptations that keep aerobic respiration going

Rapid upward growth
  • Rapid upward growth some rice types grow quickly away from the waterline.
  • Leaves stay above the water.
  • Stomata keep access to oxygen and carbon dioxide.
Aerenchyma
  • Aerenchyma rice stems and roots contain tissue with large air spaces.
  • Gases entering through the stomata diffuse along the air spaces to submerged parts.
  • Oxygen and carbon dioxide can be held in this tissue even when the plant is underwater.
  • Gases can be transferred from parts with access to air to parts without it.

Part 3 of 5Adaptations for anaerobic respiration

Switch
  • Switch when aerobic respiration cannot supply enough ATP, plants use anaerobic respiration.
Ethanol fermentation
  • Ethanol fermentation plants make ethanol and CO2 from pyruvate.
Toxic ethanol
  • Toxic ethanol ethanol builds up in the tissues and damages them.
Higher tolerance
  • Higher tolerance rice tolerates higher levels of ethanol than other plants.
Ethanol dehydrogenase
  • Ethanol dehydrogenase rice makes more of the enzyme that breaks down ethanol.
Result
  • Result rice can respire anaerobically for longer, making enough ATP to survive and keep growing.

Part 4 of 5Paddy fields

Deliberate flooding
  • Deliberate flooding farmers grow rice in flooded paddies.
Higher yield
  • Higher yield competing plants and weeds cannot survive the flooding.
Resources
  • Resources rice receives more nutrients and light.
Selection pressure
  • Selection pressure flooding removes competitors from the growing area.

Part 5 of 5More from the specification

1
Ethanol fermentation in cultivated yeast and rice
  • Ethanol fermentation in cultivated yeast and rice anaerobic respiration in flooded roots utilizes alcohol dehydrogenase whose protective enzymatic function prevents toxicity.
2
Oxidative phosphorylation
  • ATP production driven by the electron transport chain.
3
Substrate concentration
  • The amount of substrate per unit volume.
4
Intermembrane space
  • The gap between the two membranes where protons accumulate.
5
Mitochondria
  • Organelles where most aerobic respiration takes place.
6
Glucose
  • A simple sugar; the unit that starch, glycogen and cellulose are built from.
7
Glycolysis
  • Splitting of glucose to pyruvate in the cytoplasm.
8
Phosphorylation
  • Adding a phosphate group.
9
Substrate
  • The molecule that an enzyme acts on and which binds to the active site.
10
Matrix
  • The solution inside the inner membrane containing Krebs cycle enzymes.
11
Lactate
  • The product of anaerobic respiration in human cells.
12
Krebs cycle
  • Cycle in the mitochondrial matrix producing NADH, FADH2, ATP and CO2.
13
Without oxygen
  • Without oxygen reduced NAD and FAD cannot hand on their hydrogens at the electron transport chain, so they are not regenerated.

Key terms

TermMeaning
AerenchymaPlant tissue with large air spaces that carries gases through stems and roots.
Ethanol fermentationAnaerobic pathway in which pyruvate is converted to ethanol and CO2.
Ethanol dehydrogenaseEnzyme that breaks down ethanol.
WaterloggingSoil or roots covered by water so little oxygen reaches them.
Paddy fieldDeliberately flooded field used to grow rice.

Avoid these mistakes

Avoid these mistakes
Saying aerenchyma stores oxygen only — it is a continuous air-space tissue that lets gases diffuse to submerged parts.
Saying rice does not need oxygen — it still respires aerobically where gas reaches, and also tolerates ethanol.
Forgetting ethanol is toxic — the adaptation is tolerance and extra ethanol dehydrogenase, not avoiding ethanol.

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